Etch stop layer in poly-metal structures

ABSTRACT

In accordance with one embodiment of the present invention, a method of interfacing a poly-metal stack and a semiconductor substrate is provided where an etch stop layer is provided in a polysilicon region of the stack. The present invention also addresses the relative location of the etch stop layer in the polysilicon region and a variety of stack materials and oxidation methods. The etch stop layer may be patterned within the poly or may be a continuous conductive etch stop layer in the poly. The present invention also relates more broadly to a process for forming wordline architecture of a memory cell. In accordance with another embodiment of the present invention, a semiconductor structure is provided comprising a poly-metal stack formed over a semiconductor substrate where the interface between an oxidation barrier placed over the stack and an oxidized portion of the stack lies along the sidewall of the poly. A semiconductor structure is also provided where a conductive layer is present in the poly region of the poly-metal stack. The present invention also relates more broadly to a memory cell array and a computer system including the poly-metal stack of the present invention.

CROSS REFERENCE OF RELATED APPLICATIONS

The present application, U.S. patent application Ser. No. 10/438,360 (MIO 0086 VA/00-1137.01) is a divisonal application and claims priority to parent U.S. patent application Ser. No. 09/971,250, filed Oct. 4, 2001, now U.S. Pat. No. 6,699,777 (MIO 0086 PA/00-1137.01). The family of related applications claiming priority to the above-noted parent application is as follows: U.S. patent application Ser. No. 10/438,360 (MIO 0086 VA/004137.01), which is a division of the above-noted parent application; U.S. patent application Ser. No. 10/633,165 (MIO 0086 NA/00-1137.02), which is a continuation of the above-noted parent application; U.S. patent application Ser. No. 10/894,292 (MIO 0086 V2/00-1137.03), which is a division of U.S. patent application Ser. No. 10/438,360 (MIO 0086 VA/00-1137.01); and U.S. patent application Ser. No. 10/920,848 (MIO 0086 V3/00-1137.04), which is a division of U.S. patent application Ser. No. 10/438,360 (MIO 0086 VA/00-1137.01).

BACKGROUND OF THE INVENTION

The present invention relates to stacked poly-metal structures in semiconductor devices and to processes related to the formation of such structures. The present invention is particularly relevant to the wordline architecture of a DRAM cell, but is also related in a more general sense to the gate conductor architecture of a transistor. The present invention arises from the continuing need in the art for improvements to the materials and processes utilized in semiconductor device fabrication.

BRIEF SUMMARY OF THE INVENTION

Many conductors are particularly well suited for use in semiconductor devices. For example, tungsten and other metals are often used as a part of the wordline architecture of a DRAM cell. Unfortunately, many of these otherwise preferable conductors are also difficult to incorporate in certain device architecture because they are subject to severe degradation during the oxidation steps commonly utilized to construct many semiconductor devices. A number of processing techniques can limit this type of degradation. For example, in the context of the wordline architecture of a DRAM cell, manufacturing steps directed to the formation of oxidation barrier layers are introduced to protect the conductors of the wordline architecture from oxidation. The present invention is directed to improving these manufacturing steps by providing an etch stop layer in a silicon substrate of a semiconductor device. More specifically, the present invention is directed to improving manufacturing steps by providing an etch stop layer in a silicon substrate over which the wordline architecture of a DRAM cell is formed.

In accordance with one embodiment of the present invention, a method of interfacing a poly-metal stack and a semiconductor substrate is provided where an etch stop layer is provided in a polysilicon region of the stack. The present invention also addresses the relative location of the etch stop layer in the polysilicon region and a variety of stack materials and oxidation methods. The etch stop layer may be patterned within the poly or may be a continuous conductive etch stop layer in the poly. The present invention also relates more broadly to a process for forming wordline architecture of a memory cell.

In accordance with another embodiment of the present invention, a semiconductor structure is provided comprising a poly-metal stack formed over a semiconductor substrate where the interface between an oxidation barrier placed over the stack and an oxidized portion of the stack lies along the sidewall of the poly. A semiconductor structure is also provided where a conductive layer is present in the poly region of the poly-metal stack. The present invention also relates more broadly to a memory cell array and a computer system including the poly-metal stack of the present invention.

Accordingly, it is an object of the present invention to provide for improvements to the materials and processes utilized in semiconductor device fabrication. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of the preferred embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

FIGS. 1-5 illustrate a method of interfacing a poly-metal stack and a semiconductor substrate according to one embodiment of the present invention;

FIGS. 6-9 illustrate a method of interfacing a poly-metal stack and a semiconductor substrate according to another embodiment of the present invention;

FIGS. 10-13 illustrate a variety of etch stop layers for use in the method of the present invention;

FIGS. 14-19 illustrate a variety of poly-metal structure configurations for use in the method of the present invention;

FIG. 19 is a general schematic illustration of a memory cell array according to the present invention; and

FIG. 20 is a general schematic illustration of a computer system according to the present invention.

DETAILED DESCRIPTION

Referring initially to FIGS. 1-5, a method of interfacing a poly-metal stack 100 and a semiconductor substrate 102 according to one embodiment of the present invention is illustrated. Initially, referring to FIG. 1, a multi-layer poly-metal structure is formed over the semiconductor substrate 102. As will be appreciated by those skilled in the art of semiconductor fabrication, a variety of components may be utilized to form a poly-metal structure for use in a memory device. In the illustrated embodiment, the poly-metal structure initially includes a gate dielectric or other oxide layer 106, a polysilicon layer or region 108, a barrier layer 110, a metal layer 112, typically tungsten, and a silicon dioxide layer 114. Conventional isolation regions 104 are also illustrated. The oxide layer 106 typically comprises a silicon dioxide layer. The present invention is particularly advantageous in the context of tungsten-based metal layers 112 because it relates to a process by which the metal layer may be shielded from oxidation in a precise manner.

Referring specifically to FIG. 2, an etch stop layer 122 is formed in the polysilicon region 108 of the poly-metal structure with the aid of a masking layer 120. The etch stop layer 122 may be formed through ion implantation of oxygen or nitrogen, to form a SiOx or a SiNx etch stop layer 122 in the polysilicon region 108. The patterned etch stop layer 122 may also be formed through implantation of carbon, fluorine or any other suitable material capable of forming an etch stop layer in cooperation with polysilicon. It is noted that the polysilicon region 108 is typically doped to render it conductive. It is also noted that the etch stop layer 122 is described herein as patterned in the sense that it forms a non-continuous layer relative to the surface of the semiconductor substrate 102.

As is illustrated in FIG. 3, portions of the poly-metal structure extending from an upper surface 124 of the poly-metal structure to the etch stop layer 122 are removed to form a partial poly-metal stack 101 including an exposed metal region 112′ along a sidewall of the stack 101. Portions of the polysilicon layer 108, the barrier layer 110, and the silicon dioxide layer 114 are also exposed along the sidewall of the stack 101.

Next, as is illustrated in FIG. 4, the exposed metal region 112′ is covered with an oxidation barrier layer or sidewall spacer 115. The barrier layer 115 may comprise a nitride, an oxide, or a layer of oxide and a layer of nitride.

Finally, referring to FIG. 5, the etch stop layer 122, or at least portions thereof, are removed to expose a region of the oxide layer 106 along the sidewall, forming a full poly-metal stack 100. The poly-metal stack 100 and the semiconductor substrate 102 are interfaced by subjecting the exposed regions of the oxide layer 106 and the polysilicon layer 108 to an oxidation process. The oxidation process forms an oxidized layer 118 along the exposed oxide and polysilicon regions. The oxidized layer 118 and the oxidation barrier layer 115 interface along the sidewall at a boundary 117 defined between upper and lower polysilicon regions 108A, 108B of the polysilicon layer 108.

The position of the etch stop layer 122 can be controlled with great precision. The position of the boundary 117 is a direct function of the position of the etch stop layer 122 and defines specific operating characteristics of the associated semiconductor device. Accordingly, the process illustrated in FIGS. 1-5 is particularly advantageous in large scale, multi-cell semiconductor device manufacture because operational uniformity across the entire device may be optimized by controlling the point at which the boundary 117 lies along the sidewall of the stack 100 with great precision.

The process illustrated in FIGS. 6-9 is similar to that illustrated in FIGS. 1-5 with the exception that the etch stop layer 122 is formed as a continuous layer of conductive material in the polysilicon layer 108. The continuous layer may be formed by providing the polysilicon layer 108 in a plurality of structural layering steps and forming the etch stop layer 122 in the polysilicon region through an intermediate layering step. The conductive etch stop layer 122 may be formed from silicon and germanium or any other material or combination of materials suitable for use as a conductive etch stop layer. The dopant present in the polysilicon region 108 of the poly-metal structure may be used to form the conductive etch stop layer 122 by forming the etch stop layer 122 of a material that will accept transfer of a quantity of the dopant from the polysilicon region 108 to the etch stop layer 122.

Conventional CMOS integrated circuits utilizing clad silicide on moats suffer from potential leakage paths along the sidewall surface of the etched polysilicon gates, a region where the electrical field strength is high due to enhanced electric field lines at the edge of the polysilicon conductor. Many types of semiconductor devices, such as DRAMs and EPROMs minimize this problem by oxidizing the gate polysilicon after the gate etch to form a high quality interface at the edge of the polysilicon. Enhanced oxidation under the gate edge is often referred to as the smile effect. The irregular shape of the oxidized layer 118 in FIGS. 5 and 9 is intended to highlight the smile effect.

In the context of the present invention, the poly-metal stack 100 and the semiconductor substrate 102 of the present invention may be interfaced through selective or non-selective oxidation. Preferably, the poly-metal stack 100 and the semiconductor substrate are interfaced through oxidation by O₂; H₂O; H₂ and H₂O; H₂ and O₂; H₂ and O₂; H₂ and activated O₂ and O₃; or combinations thereof. The oxidants may be accompanied by argon or helium. H₂ and H₂O oxidants may be derived from catalytic conversion of H₂ and O₂. Activated O₂ may be derived through activation by a remote plasma unit.

For the purposes of describing and defining the present invention, it is noted that an etch stop layer formed “in” the polysilicon region may be formed at a surface of the polysilicon region or within the polysilicon region between its upper and lower surfaces. A layer formed “at” a surface of a region may be formed directly on the surface or may be partially embedded in the region so as to define a portion of the surface of the region. In the embodiment of FIGS. 2 and 6, the etch stop layer 122 is formed within the polysilicon layer 108. It should be further noted that, for the purposes of defining and describing the present invention, “on” a substrate or layer denotes formation in contact with the surface of the substrate or layer and “over” a substrate or layer denotes formation above or in contact with the surface of the substrate or layer.

Referring now to FIGS. 10 and 12, it is noted that the etch stop layer of FIGS. 2 and 6 may be formed at an upper surface of the polysilicon region 108. Similarly, referring to FIGS. 11 and 13, the etch stop layer 122 may be formed at a lower surface of the polysilicon region 108.

For the purposes of defining and describing the present invention, it is noted that a poly-metal structure comprises a structure that includes a polysilicon region and a metal region. The poly-metal structure may include materials or regions in addition to the polysilicon region and the metal region. The polysilicon region may be doped or undoped and the metal region may be a pure metal, e.g. tungsten, or a metal-based material, e.g., tungsten, a tungsten-containing alloy, tungsten nitride, tungsten silicide, etc. As is noted above, a variety of components may be utilized to form a poly-metal structure for use in a memory device according to the present invention.

In the embodiment illustrated in FIGS. 1, 6, and 10-13, the poly-metal structure comprises a gate dielectric or other oxide layer 106, a polysilicon layer or region 108, a barrier layer 110, a metal layer 112, and a silicon dioxide layer 114. However, it is noted that a variety of additional poly-metal structures fall within the scope of the present invention. For example, referring to FIG. 14, the silicon dioxide layer 114 may be replaced by a layer 114′ of Si₃N₄ or any other suitable material. Similarly, the barrier layer 110, which may comprise tungsten nitride, tungsten silicide, tungsten silicide nitride, titanium nitride, titanium silicide nitride, and combinations thereof may be replaced by one or more alternative layers or may be accompanied by additional layers of different materials.

Referring to FIG. 14, for example, the metal layer 112 may comprise tungsten and the barrier layer 110 may comprise tungsten nitride or tungsten silicide nitride. Alternatively, referring to FIG. 15, a titanium nitride layer 111 may be provided between the polysilicon layer 108 and a tungsten nitride layer 110. Referring to FIGS. 16 and 17, it is noted that the metal layer 112 may comprise tungsten and the barrier layer may comprise a titanium nitride layer 111 or a titanium nitride layer 111 in combination with a titanium suicide nitride layer 113. Referring to FIG. 18, the poly-metal structure may be formed such that the metal layer 112 comprises tungsten and the barrier layer comprises tungsten silicide nitride 110 formed over tungsten silicide 109. Finally, referring to FIG. 19, it is noted that a barrier layer 110, e.g., tungsten nitride, may be interposed between a pair of metal layers 112, e.g., tungsten. In many instances, a tungsten nitride layer may be interposed between the tungsten layer 112 and the barrier layer 110.

FIG. 20 illustrates a top view layout of a memory device 100′ including wordlines 104′, digitlines 102′, and a unit cell or memory cell 101′. The unit cell or memory cell 101′ is one of many cells of the memory device 100′. The memory cell 101′ illustrated in FIG. 20 has a feature size 105′ in a first dimension that is half of the digitline pitch and a feature size 106′ in a second dimension which matches the wordline pitch. It is noted that the present invention is not, however, limited to memory cells of a particular feature size. Nor is the present invention limited to particular wordline, digitline, or memory cell layout or geometry.

FIG. 21 is an illustration of a computer system 10 that can use and be used with embodiments of the present invention. The computer system 10 can be a desktop, network server, handheld computer or the like. As will be appreciated by those skilled in the art, the computer system 10 would include ROM 14, mass memory 16, peripheral devices 18, and I/O devices 20 in communication with a microprocessor or programmable controller 22 via a data bus 24 or another suitable data communication path. The memory devices 14 and 16 can be fabricated according to the various embodiments of the present invention. ROM 14 can include EPROM, EEPROM, flash memory, or any other suitable ROM. Mass memory 16 can include DRAM, synchronous RAM, flash memory, or any other suitable mass memory.

Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention. 

1. A method of niterfacing a poly-metal stack and a semiconductor substrate by: forming a multi-layer poly-metal structure over said semiconductor substrate, wherein said poly-metal structure includes a patterned etch stop layer formed in a polysilicon region of said poly-metal structure; removing portions of said poly-metal structure extending from an upper surface of said poly-metal structure to said patterned etch stop layer to form a partial poly-metal stack including an exposed metal region along a sidewall of said stack; covering said exposed metal region with an oxidation barrier layer; removing said patterned etch stop layer to form a full poly-metal stack including an exposed oxide region along a sidewall of said slack; and interfacing said poly-metal stack and said semiconductor substrate by subjecting said exposed oxide region to an oxidation process.
 2. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said etch stop layer is formed within said polysilicon region.
 3. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 2 wherein: said partial poly-metal stack is farmed to include an exposed metal region along a sidewall of said stack and an exposed upper polysilicon region along a sidewall of said stack; said exposed metal region and said exposed upper polysilicon region are covered with an oxidation barrier layer; said full poly-metal stack is farmed to include an exposed lower polysilicon region along a sidewall of said stack and an exposed oxide region along a sidewall of said stack; and said poly-metal stack and said semiconductor substrate are interfaced by subjecting said exposed lower polysilicon region and said exposed oxide region to an oxidation process.
 4. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein: said etch stop layer is formed at an upper surface of said polysilicon region; said full poly-metal stack is further formed by removing at least a portion of said etch stop layer and a portion of said polysilicon region to form an exposed polysilicon region; and said poly-metal stack and said semiconductor substrate are interfaced by subjecting said exposed oxide region and said exposed polysilicon region to an oxidation process.
 5. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein: said etch stop layer is formed at a lower surface of said polysilicon region; said partial poly-metal stack is further formed by removing at least a portion of said polysilicon region to form an exposed polysilicon region; and said exposed polysilicon region is covered with said oxidation barrier layer; and said poly-metal stack and said semiconductor substrate are interfaced by subjecting said exposed oxide region to said oxidation process.
 6. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said etch stop layer is formed in said polysilicon region through ion implantation.
 7. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein: said poly-metal structure is formed through a plurality of structural layering steps; and said etch stop layer is formed in said polysilicon region through an intermediate layering step of said plurality of layering steps.
 8. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said poly-metal stack and said semiconductor substrate are interfaced through oxidation by one of the following oxidants: O₂; H₂O; H₂ and H₂O; H₂ and O₂; H₂ and activated O₂; H₂ and O₃; and combinations thereof.
 9. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 8 wherein said oxidants are accompanied by argon or helium.
 10. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said poly-metal stack and said semiconductor substrate are interfaced through selective oxidation.
 11. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said poly-metal stack and said semiconductor substrate are interfaced through non-selective oxidation.
 12. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said poly-metal stack and said semiconductor substrate are interfaced through oxidation by H₂ and H₂O derived from catalytic conversion of H₂ and O₂.
 13. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein: said poly-metal stack and said semiconductor substrate are interfaced through oxidation by H₂ and activated O₂; and said activated O₂ is derived through activation by a remote plasma unit.
 14. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said poly-metal structure comprises a metal layer formed over a polysilicon layer formed over an oxide layer.
 15. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 1 wherein said poly-metal structure comprises a metal layer formed over a barrier layer formed over a polysilicon layer formed over an oxide layer.
 16. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten.
 17. A method interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said barrier layer is selected from layers of tungsten nitride, tungsten silicide, tungsten silicide nitride, titanium nitride, titanium silicide nitride, and combinations of layers thereof.
 18. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said barrier layer comprises a plurality of layers of different barrier materials.
 19. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten and said barrier layer comprises a tungsten nitride.
 20. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten and said barrier layer comprises a tungsten silicide nitride.
 21. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten and said barrier layer comprises a titanium nitride.
 22. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten and said barrier layer comprises a tungsten nitride layer over a titanium nitride layer.
 23. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten and said barrier layer comprises a titanium nitride layer over a titanium silicide nitride layer.
 24. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in clam 13 wherein said poly-metal structure is formed so as to further comprise a tungsten nitride layer interposed between said tungsten layer and said barrier layer.
 25. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises tungsten and said barrier layer comprises tungsten silicide nitride formed over tungsten silicide.
 26. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises a barrier layer interposed between a pair of tungsten layers.
 27. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 15 wherein said poly-metal structure is formed such that said metal layer comprises a tungsten nitride layer interposed between a pair of tungsten layers.
 28. A method of interfacing a poly-metal stack and a semiconductor substrate by: forming a multi-layer poly-metal structure over said semiconductor substrate; forming a patterned etch stop layer in a polysilicon region of said poly-metal structure through ion implantation; removing portions of said poly-metal structure extending from an upper surface of said poly-metal structure to said patterned etch stop layer to form a partial poly-metal stack including an exposed metal region along a sidewall of said stack; covering said exposed metal region with an oxidation barrier layer; removing said patterned etch atop layer to form a full poly-metal stack including an exposed oxide region along a sidewall of said stack; and interfacing said poly-metal stack and said semiconductor substrate by subjecting said exposed oxide region to arm oxidation process.
 29. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 28 wherein said patterned etch stop layer is formed through implantation of nitrogen or oxygen into said polysilicon layer to form a SiO_(x) or a SiN_(x) etch stop layer in said polysilicon region.
 30. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 28 wherein said patterned etch stop layer is formed through implantation of carbon or fluorine into said polysilicon layer.
 31. A method of interfacing a poly-metal stack and a semiconductor substrate by: forming a multi-layer poly-metal structure over said semiconductor substrate, wherein said poly-metal structure includes a conductive etch stop layer formed in a polysilicon region of said poly-metal structure; removing portions of said poly-metal structure extending from an upper surface of said poly-metal structure to said etch stop layer to form a partial poly-metal stack including an exposed metal region along a sidewall of said stack; covering said exposed metal region with an oxidation barrier layer; removing portions of said etch stop layer to form a full poly-metal stack including an exposed oxide region along a sidewall of said stack; and interfacing said poly-metal stack and said semiconductor substrate by subjecting said exposed oxide region to an oxidation process.
 32. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 31 wherein said conductive etch stop layer is formed from silicon and germanium.
 33. A method of interfacing a poly-metal stack and a semiconductor substrate as claimed in claim 31 wherein said polysilicon region of said poly-metal structure contains a dopant and wherein said conductive etch stop layer is formed so as to accept transfer of a quantity of said dopant from said polysilicon region to said etch stop layer.
 34. A method of providing operational uniformity across a multi-memory cell semiconductive device, said method comprising: providing a semiconductor substrate; forming a first oxide layer on said semiconductor substrate; forming an polysilicon layer on said oxide layer; forming a barrier layer on said polysilicon layer; forming a metal layer on said barrier layer; forming a second oxide layer on said metal layer; providing a masking layer over portions of said second oxide layer; implanting ions into said polysilicon layer to form at least one etch stop layer; etching said substrate to said etch stop layer, said portions covered by said masking layer defining poly-metal structures on said oxide layer, said poly-metal structure includes a metal region, a polysilicon region, and an oxide region; forming an oxidation barrier layer on exposed portions of said metal region and said polysilicon region; etching said substrate to said oxide layer adjacent said poly-metal structures; and oxidizing said substrate such that an oxidized layer forms on a remaining exposed portion of said polysilicon region, said oxide barrier layer and said oxidized layer define sidewalls, and said oxidized layer and said oxidation barrier layer interface along said sidewall, at a point defined by said conductive etch stop layer. 